Conventionally, there are known scroll-type compressors in which a compression chamber is formed by compression-chamber-forming members such as a fixed scroll and a movable scroll. For example, there have been scroll-type compressors in which a refrigerant gas at intermediate pressure in a refrigeration cycle is injected into the compression chamber, whereby the operating efficiency of an air conditioner is improved (see, e.g., Japanese Laid-open Patent Publication No. H11-107950). There have been scroll-type compressors in which a back pressure chamber is provided to a rear-surface side of the movable scroll, and overturning of the movable scroll is suppressed by applying a pressing force in a direction opposite a thrust-direction gas load in a compression chamber (see, e.g., Japanese Laid-open Patent Publication No. 2012-117519).